Liquid crystal display device

ABSTRACT

The present invention provides a liquid crystal display device comprising at least: a backlight; a polarizer; a first optically anisotropic layer with a retardation of 210 to 300 nm at a wavelength of 550 nm; a second optically anisotropic layer with a retardation of 50 to 140 nm at a wavelength of 550 nm; a third optically anisotropic layer with negative optical anisotropy; a liquid crystal cell comprising upper and lower substrates facing each other and a liquid crystal layer sandwiched between the upper and lower substrates; a fourth optically anisotropic layer with a retardation of 50 to 140 nm at a wavelength of 550 nm; a first optically anisotropic layer with a retardation of 210 to 300 nm at a wavelength of 550 nm; and a polarizer, arranged in piles in this order from the backlight, the second optically anisotropic layer comprising at least a liquid crystal film with a fixed nematic hybrid liquid crystal orientation structure. The liquid crystal display device provides bright images and is high in contrast and less in viewing angle dependency.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Section 371 of International Application No.PCT/JP2006/322406, filed Nov. 2, 2006, which was published in theJapanese language on Aug. 2, 2007, under International Publication No.WO 2007/086179 A1 and the disclosure of which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

The present invention relates to liquid crystal display devices ortransflective liquid crystal display devices having both reflective andtransmissive mode, used for office automation (OA) equipment such asword processors and personal computers, mobile information terminalssuch as personal digital assistants and mobile telephones, or camcordersequipped with a liquid crystal monitor.

Liquid crystal display devices are classified broadly into those capableof displaying images in a reflective mode, those capable of displayingimages in transmissive mode, and those of capable of displaying imagesin both reflective and transmissive modes and have been used widely asdisplay devices for lap top computers or televisions because of theirlow-profile and light weight characteristics. In particular, thetransflective liquid crystal display devices use a display mode capableof displaying images both in reflective and transmissive modes and thuscan display images in a well-lighted area or a dark area and reduce theelectric power consumption by switching to either one of the reflectiveand transmissive modes, depending on the brightness in the environment.Therefore, the transflective liquid crystal display devices have beenused for various mobile information terminals.

The transmissive, reflective and transflective liquid crystal displaydevices in particular in the transmissive mode can not avoid problemsconcerning viewing angle such as reduced display contrast, changes indisplay color and reversed gradation occurring when viewed obliquelybecause of the refractive index anisotropy of the liquid crystalmolecules and thus has been demanded to be improved in these regards.

For a transmissive liquid crystal display device using a TN mode(twisted angle of liquid crystal is 90 degrees), a method for solvingthese problems has been proposed and practically used wherein opticalcompensation films are disposed between the liquid crystal cell and eachof the upper and lower polarizers.

For example, there are known some structures wherein an opticalcompensation film composed of a hybrid-aligned discotic liquid crystalor a nematic hybrid-aligned liquid crystalline polymer compound isdisposed between the liquid crystal cell and each of the upper and lowerpolarizers (Patent Document Nos. 1 to 3 below).

For a transflective liquid crystal display device, it is necessary todispose a circular polarizer comprising one or a plurality of uniaxiallyretardation film in displaying principle and a polarizer above or belowthe liquid crystal cell for the transmissive mode.

In order to enlarge the viewing angle of the transflective liquidcrystal device in the transmissive mode, a method has been proposed andpractically used wherein an optical compensation film aligned in anematic hybrid orientation is used as a circular polarizer to bedisposed between the liquid crystal cell and the backlight (see PatentDocument Nos. 4 and 5).

(1) Patent Document No. 1: Japanese Patent Publication No. 2640083

(2) Patent Document No. 2: Japanese Laid-Open Publication No. 11-194325

(3) Patent Document No. 3: Japanese Laid-Open Publication No. 11-194371

(4) Patent Document No. 4: Japanese Laid-Open Publication No. 2002-31717

(5) Patent Document No. 5: Japanese Laid-Open Publication No.2004-157454

BRIEF SUMMARY OF THE INVENTION

However, the foregoing methods can not solve the above-describedproblems concerning the viewing angle, such as reduced display contrast,changes in display color and reversed gradation occurring when theliquid crystal display device is viewed obliquely. In particular, it isessentially difficult for the transflective liquid crystal displaydevice to improve the viewing angle because of the use of a circularpolarizer comprising one or a plurality of stretched film in principleand a polarizer.

In view of the foregoing problems, the present invention has an objectto provide a liquid crystal display device which can provide brightimages and is high in contrast and less in viewing angle dependency. Thepresent invention also has an object to provide a transflective liquidcrystal display device which can provide bright image and is high incontrast and less in viewing angle dependency in the transmissive mode,by arranging a reflective layer on part of the liquid crystal cell.

That is, according to a first aspect of the present invention, there isprovided a liquid crystal display device comprising at least: abacklight; a polarizer; a first optically anisotropic layer with aretardation of 210 to 300 nm at a wavelength of 550 nm; a secondoptically anisotropic layer with a retardation of 50 to 140 nm at awavelength of 550 nm; a third optically anisotropic layer with negativeoptical anisotropy; a liquid crystal cell comprising upper and lowersubstrates facing each other and a liquid crystal layer sandwichedbetween the upper and lower substrates; a fourth optically anisotropiclayer with a retardation of 50 to 140 nm at a wavelength of 550 nm; afirst optically anisotropic layer with a retardation of 210 to 300 nm ata wavelength of 550 nm; and a polarizer, arranged in piles in this orderfrom the backlight, the second optically anisotropic layer comprising atleast a liquid crystal film with a fixed nematic hybrid liquid crystalorientation structure.

According to a second aspect of the present invention, there is provideda liquid crystal display device comprising at least: a backlight; apolarizer; a first optically anisotropic layer with a retardation of 210to 300 nm at a wavelength of 550 nm; a second optically anisotropiclayer with a retardation of 50 to 140 nm at a wavelength of 550 nm; aliquid crystal cell comprising upper and lower substrates facing eachother and a liquid crystal layer sandwiched between the upper and lowersubstrates; a third optically anisotropic layer with negative opticalanisotropy; a fourth optically anisotropic layer with a retardation of50 to 140 nm at a wavelength of 550 nm; a first optically anisotropiclayer with a retardation of 210 to 300 nm at a wavelength of 550 nm; anda polarizer, arranged in piles in this order from the backlight, thesecond optically anisotropic layer comprising at least a liquid crystalfilm with a fixed nematic hybrid liquid crystal orientation structure.

According to a third aspect of the present invention, there is provideda liquid crystal display device comprising at least: a backlight; apolarizer; a first optically anisotropic layer with a retardation of 210to 300 nm at a wavelength of 550 nm; a fourth optically anisotropiclayer with a retardation of 50 to 140 nm at a wavelength of 550 nm; athird optically anisotropic layer with negative optical anisotropy; aliquid crystal cell comprising upper and lower substrates facing eachother and a liquid crystal layer sandwiched between the upper and lowersubstrates; a second optically anisotropic layer with a retardation of50 to 140 nm at a wavelength of 550 nm; a first optically anisotropiclayer with a retardation of 210 to 300 nm at a wavelength of 550 nm; anda polarizer, arranged in piles in this order from the backlight, thesecond optically anisotropic layer comprising at least a liquid crystalfilm with a fixed nematic hybrid liquid crystal orientation structure.

According to a fourth aspect of the present invention, there is provideda liquid crystal display device comprising at least: a backlight; apolarizer; a first optically anisotropic layer with a retardation of 210to 300 nm at a wavelength of 550 nm; a fourth optically anisotropiclayer with a retardation of 50 to 140 nm at a wavelength of 550 nm; aliquid crystal cell comprising upper and lower substrates facing eachother and a liquid crystal layer sandwiched between the upper and lowersubstrates; a third optically anisotropic layer with negative opticalanisotropy; a second optically anisotropic layer with a retardation of50 to 140 nm at a wavelength of 550 nm; a first optically anisotropiclayer with a retardation of 210 to 300 nm at a wavelength of 550 nm; anda polarizer, arranged in piles in this order from the backlight, thesecond optically anisotropic layer comprising at least a liquid crystalfilm with a fixed nematic hybrid liquid crystal orientation structure.

According to a fifth aspect of the present invention, there is providedthe liquid crystal display device according to any one of the first tofourth aspects, wherein the liquid crystal layer is of a twisted nematicmode.

According to a sixth aspect of the present invention, there is providedthe liquid crystal display device according to any one of the first tofourth aspects, wherein the liquid crystal layer is of a parallelorientation with a twist angle of 0 degrees.

According to a seventh aspect of the present invention, there isprovided the liquid crystal display device according to any one of thefirst to fourth aspects, wherein the third optically anisotropic layerfulfills the requirement set forth in formula (1) and has a planedirection retardation (Re) in the range of 0 nm to 30 nm and a thicknessdirection retardation (Rth) in the range of −200 nm to −30 nm, both at awavelength of 550 nm, when (Re) and (Rth) are represented by formulas(2) and (3), respectively:nx≧ny>nz  (1)Re=(nx−ny)×d  (2)Rth={nz(nx+ny)/2}×d  (3)wherein nx and ny denote principal indices of plane direction refractionof the optically anisotropic layer, nz denotes a principal index ofthickness direction refraction of the optically anisotropic layer, and ddenotes the thickness (nm) thereof.

According to an eighth aspect of the present invention, there isprovided the liquid crystal display device according to any one of thefirst to fourth aspects, wherein the third optically anisotropic layeris formed from at least one type of material selected from the groupconsisting of liquid crystalline compounds, triacetyl cellulose,polyamides, polyimides, polyesters, polyether ketones, polyamide imides,and cyclic olefin polymers.

According to a ninth aspect of the present invention, there is providedthe liquid crystal display device according to any one of the first tofourth aspects, wherein the first and fourth optically anisotropiclayers are stretched polymer films.

According to a tenth aspect of the present invention, there is providedthat liquid crystal display device according to any one of the first tofourth aspects, wherein the first and fourth optically anisotropiclayers are each a liquid crystal film produced by fixing a liquidcrystalline substance exhibiting an optically positive uniaxiality, in anematic orientation formed when the substance is in the liquid crystalstate.

According to an eleventh aspect of the present invention, there isprovided the liquid crystal display device according to any one of thefirst to fourth aspects, wherein the angle defined by the tilt directionof the hybrid direction of the liquid crystal film forming the secondoptically anisotropic layer, projected to a plane and the rubbingdirection of the liquid crystal layer is in the range of 0 to 30degrees.

According to a twelfth aspect of the present invention, there isprovided the liquid crystal display device according to any one of thefirst to fourth aspects, wherein the second optically anisotropic layeris a liquid crystal film produced by fixing a liquid crystallinesubstance exhibiting an optically positive uniaxiality, in a nematichybrid orientation formed when the substance is in the liquid crystalstate, and the average tilt angle of the nematic hybrid orientation isin the range of 36 to 45 degrees.

According to a thirteenth aspect of the present invention, there isprovided the liquid crystal display device according to any one of thefirst to seventh aspects, wherein the lower substrate of the liquidcrystal cell has a transflective electrode on which a region with areflective function and a region with a transmissive function areformed.

According to a fourteenth aspect of the present invention, there isprovided the liquid crystal display device according to the thirteenthaspect, wherein the thickness of the liquid crystal layer on the regionwith a reflective function in the liquid crystal cell is smaller thanthat of the liquid crystal layer on the region with a transmissivefunction.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The foregoing summary, as well as the following detailed description ofthe invention, will be better understood when read in conjunction withthe appended drawings. For the purpose of illustrating the invention,there are shown in the drawings embodiments which are presentlypreferred. It should be understood, however, that the invention is notlimited to the precise arrangements and instrumentalities shown.

In the drawings:

FIG. 1 is a conceptual view for describing the tilt and twisted anglesof a liquid crystal molecule.

FIG. 2 is a conceptual view for describing the aligned structure of theliquid crystal film forming the second optically anisotropic layer.

FIG. 3 is a conceptual view for describing the pre-tilt direction of theliquid crystal cell.

FIG. 4 is a schematic cross-sectional view of the liquid crystal displaydevice of Example 1.

FIG. 5 is a plan view indicating the angular relation of the absorptionaxes of the polarizers, the pre-tilt direction of the liquid crystalcell, the slow axes of the polymeric stretched films and the tiltdirection of the liquid crystal film in Example 1.

FIG. 6 is a view indicating the contrast ratio when viewing the liquidcrystal display device of Example 1 from all the directions.

FIG. 7 is a schematic cross-sectional view of the liquid crystal displaydevice of Example 2.

FIG. 8 is a plan view indicating the angular relation of the absorptionaxes of the polarizers, the pre-tilt direction of the liquid crystalcell, the slow axes of the polymeric stretched films and the tiltdirection of the liquid crystal film in Example 2.

FIG. 9 is a view indicating the contrast ratio when viewing the liquidcrystal display device of Example 2 from all the directions.

FIG. 10 is a schematic cross-sectional view of the liquid crystaldisplay device of Example 3.

FIG. 11 is a plan view indicating the angular relation of the absorptionaxes of the polarizers, the pre-tilt direction of the liquid crystalcell, the slow axes of the polymeric stretched films and the tiltdirection of the liquid crystal film in Example 3.

FIG. 12 is a view indicating the contrast ratio when viewing the liquidcrystal display device of Example 3 from all the directions.

FIG. 13 is a schematic cross-sectional view of the liquid crystaldisplay device of Example 4.

FIG. 14 is a plan view indicating the angular relation of the absorptionaxes of the polarizers, the pre-tilt direction of the liquid crystalcell, the slow axes of the polymeric stretched films and the tiltdirection of the liquid crystal film in Example 4.

FIG. 15 is a view indicating the contrast ratio when viewing the liquidcrystal display device of Example 4 from all the directions.

FIG. 16 is a schematic cross-sectional view of the liquid crystaldisplay device of Comparative Example 1.

FIG. 17 is a view indicating the contrast ratio when viewing the liquidcrystal display device of Comparative Example 1 from all the directions.

FIG. 18 is a schematic cross-sectional view of the liquid crystaldisplay device of Comparative Example 2.

FIG. 19 is a schematic cross-sectional view of the transflective liquidcrystal display device of Example 5.

DETAILED DESCRIPTION OF THE INVENTION

The liquid crystal display device of the present invention has aconfiguration selected from the following four patterns (A) to (D) andif necessary may contain components such as a light diffusing layer, alight control film, a light guide plate and a prism sheet, on which noparticular restriction is imposed except for using the above-mentionedsecond optically anisotropic layer formed of a liquid crystal film witha fixed nematic hybrid orientation. Any of the configuration patterns(A) to (D) may be used in order to obtain optical characteristics withless viewing angle dependency:

-   -   (A) polarizer/first optically anisotropic layer/fourth optically        anisotropic layer/liquid crystal cell/third optically        anisotropic layer/second optically anisotropic layer/first        optically anisotropic layer/polarizer/backlight;    -   (B) polarizer/first optically anisotropic layer/fourth optically        anisotropic layer/third optically anisotropic layer/liquid        crystal cell/second optically anisotropic layer/first optically        anisotropic layer/polarizer/backlight    -   (C) polarizer/first optically anisotropic layer/second optically        anisotropic layer/liquid crystal cell/third optically        anisotropic layer/fourth optically anisotropic layer/first        optically anisotropic layer/polarizer/backlight    -   (D) polarizer/first optically anisotropic layer/second optically        anisotropic layer/third optically anisotropic layer/liquid        crystal cell/fourth optically anisotropic layer/first optically        anisotropic layer/polarizer/backlight.

The component parts used in the present invention will be described inorder below.

First of all, the liquid crystal cell used in the present invention willbe described.

Examples of the mode of the liquid crystal cell include TN (TwistedNematic), STN (Super Twisted Nematic), ECB (Electrically ControlledBirefringence), IPS (In-Plane Switching), VA (Vertical Alignment), OCB(Optically Compensated Birefringence), HAN (Hybrid-Aligned Nematic), ASM(Axially Symmetric Aligned Microcell), Half Tone Gray Scale mode, domaindivided mode, and display modes using a ferroelectric liquid crystal andan antiferroelectric liquid crystal. The mode of the liquid crystal cellused in the present invention is preferably an imaging mode using an ECB(electrically controlled birefringence) mode wherein the liquid crystalmolecules are homogeneously aligned. This is because when thetransmissive display part of the liquid crystal layer is thickened andthe reflective display part thereof is thinned for a TN mode or an STNmode, the difference in thickness between the both parts, if enlarged,would cause liquid crystal molecules at the boundary between the bothparts to align defectively and thus be likely to invite problems inproduction.

There is no particular restriction on the driving mode of the liquidcrystal cell, which may, therefore, be a passive matrix mode used in anSTN-LCD, an active matrix mode using active electrodes such as TFT (ThinFilm Transistor) electrodes and TFD (Thin Film Diode) electrodes, and aplasma address mode.

The liquid crystal cell is composed of a liquid crystal layer sandwichedbetween two transparent substrates disposed to face each other (theviewer's side substrate may be referred to as “upper substrate” and thebacklight side's substrate may be referred to as “lower substrate”).

There is no particular restriction on the material forming the liquidcrystal layer. Examples of the material include various low molecularweight liquid crystalline substances, polymeric liquid crystallinesubstances, and mixtures thereof, which can constitute various liquidcrystal cells. The liquid crystalline material may be blended with dyes,chiral dopants, or non-liquid crystalline substances to an extent thatthey do not prevent the liquid crystal substance from exhibiting liquidcrystallinity. The liquid crystal cell may be provided with variouscomponents required for the above-described various liquid crystal cellmodes or various components described below.

There is no particular restriction on the transparent substrates formingthe liquid crystal cell as long as they can align a liquid crystallinematerial forming a liquid crystal layer in a specific alignmentdirection. More specific examples include those which themselves have aproperty of aligning a liquid crystalline material and those whichthemselves have no capability of aligning but are provided with analignment layer capable of aligning a liquid crystalline material. Theelectrode of the liquid crystal cell may be any conventional electrode,such as ITO. The electrode may be usually arranged on the surface of thetransparent substrate, which surface contacts the liquid crystal layer.In the case of using a transparent substrate with an alignment layer, anelectrode may be provided between the alignment layer and the substrate.

The liquid crystal display device of the present invention is atransmissive liquid crystal display using a backlight. However, atransflective liquid crystal display device which can be operated inboth a reflective mode and a transmissive mode can be produced byarranging a transflective electrode provided with a region having areflection function and a region having a transmission function, on thelower substrate of the liquid crystal cell.

There is no particular restriction on the reflection layer (hereinaftermay also be referred to as “reflector”), which may, therefore, be ametal such as aluminum, silver, gold, chromium, and platinum, an alloycontaining one or more of these metals, an oxide such as magnesiumoxide, a multi-layered film of dielectrics, a liquid crystal filmexhibiting a selective reflectivity, and combinations thereof. Thesereflectors may be flat or curved and may be those provided withdiffusive reflectivity by forming rugged patterns on its surface; thosehaving a function as the electrode on the transparent substrate locatedon the side opposite to the viewer's side; or any combination thereof.

The liquid crystal cell contains a transflective layer on which a regionwith a reflection function and a region with a transmission function areformed. The region with a reflection function will be a reflectivedisplay part providing images by reflection while the region with atransmission function will be a transmissive display part providingimages by transmission.

The liquid crystal layer at the reflective display part in the liquidcrystal cell is preferably thinner than the liquid crystal layer at thetransmissive display part. The reason will be described below.

First of all, description will be given of the transmissive displayingin the transmissive display part when the thickness of the liquidcrystal layer is set to be suitable for reflection displaying. When thethickness of the liquid crystal layer is adjusted to be suitable forreflective displaying, the quantity of change in polarization caused bychanges in alignment of the liquid crystal layer by an external filedsuch as electric field is such an extent that a sufficient contrastratio is obtained by light made incident to the liquid crystal layerfrom the viewer's side and reflected at the reflector to pass throughthe liquid crystal layer again and exit to the viewer's side so that thelight goes back and forth through the liquid crystal layer. However,this setting is insufficient in quantity of change in polarization ofthe light passing through the liquid crystal layer in the transmissivedisplay part. Therefore, sufficient displaying can not be obtained inthe transmissive display part even if a polarizer to be used only fortransmissive displaying is arranged in the rear of the liquid crystalcell, viewed from the viewer in addition to the polarizer for reflectivedisplaying arranged on the viewer's side of the liquid crystal cell.That is, when the liquid crystal layer is aligned suitably for thereflective display part, the transmissive display part can not obtain asufficient contrast ratio for displaying because it lacks brightness oreven if the brightness is sufficient is not reduced in transmissivityfor dark displaying.

More specifically, upon reflective displaying, the liquid crystalorientation state in the liquid crystal layer is controlled by anapplied voltage such that a retardation of about ¼ wavelength isimparted to a light passing through the liquid crystal layer only once.Transmissive displaying effected with a liquid crystal layer with athickness suitable for reflection displaying, i.e., by effecting avoltage modulation providing a phase modulation of a ¼ wavelength cannot obtain a sufficiently bright display because the sufficientreduction of the transmittance, when the transmissive display part is ina dark display mode, causes the absorption of almost half of luminousintensity of light by the polarizer arranged on the side to which thelight is reflected. Furthermore, when optical elements such as apolarizer and an optical retardation compensator are arranged so as toincrease the luminosity upon a bright display mode of the transmissivedisplay part, the luminosity of the transmissive display part in a darkdisplay mode will be about ½ of that in the bright display mode, leadingto an insufficient contrast ratio.

Contrary to this, in order to make the thickness of the liquid crystallayer suitable for transmissive displaying, a voltage modulation must beapplied to the liquid crystal layer such that a retardation of a ½wavelength will be imparted to a light transmitting the liquid crystallayer. Therefore, in order to utilize both a reflected light and atransmitted light for a display mode with high resolution and excellentvisibility, the liquid crystal layer of the reflective display part mustbe thicker than that of the transmissive display part. Ideally, theliquid crystal layer thickness of the reflective display part is about ½of that of the transmissive display part.

The retardation of the liquid crystal cell is preferably from 200 to 400nm, more preferably from 250 to 350 nm in the transmissive display partand is preferably from 100 to 200 nm, more preferably from 120 to 180 nmin the reflective display part. The retardations of the transmissive andreflective display parts, deviating these ranges are not preferablebecause they would invite unnecessary coloration and a reduction inbrightness.

There is no particular restriction on the polarizer used in the presentinvention as long as the objects of the present invention can beachieved. Therefore, the polarizer may be any conventional one that isgenerally used in liquid crystal display devices. Specific examplesinclude PVA-based polarizing films such as polyvinyl alcohol (PVA) andpartial acetalized PVA, polarizing films such as those produced bystretching a hydrophilic polymeric film comprising a partiallysaponified product of an ethylene-vinyl acetate copolymer and absorbingiodine and/or dichroic dye, and those comprising a polyene-oriented filmsuch as a dechlorinated product of polyvinyl chloride. Alternatively,there may be used reflection type polarizers.

These polarizers may be used alone or in combination with a transparentprotective layer provided on one or both surfaces of the polarizer forthe purpose of enhancing the strength, moisture resistance, and heatresistance. Examples of the protective layer include those formed bylaminating a transparent plastic film such as polyester, triacetylcellulose or a cyclic olefin polymer directly or via an adhesive layeron the polarizer; coated layers of transparent resin; and acrylic- orepoxy-based photo-setting type resin layers. When the protective layersare coated on the both surfaces of the polarizing film, they may be thesame or different from one another.

There is no particular restriction on the first and fourth opticallyanisotropic layers used in the present invention as long as they areexcellent in transparency and uniformity. However, each of the layers ispreferably a polymeric stretched film or an optical compensation filmformed from a liquid crystalline material. Examples of the polymericstretched film include uniaxial or biaxial retardation films formed fromcellulose-, polycarbonate-, poltarylate-, polysulfone-, polyacryl,polyethersulfone-, or cyclic olefin-based polymers. The first and fourthoptically anisotropic layers exemplified herein may be composed of apolymeric stretched film or an optical film formed from a liquidcrystalline material alone or the combination thereof. Among thesepolymeric stretched films, preferred are cyclic olefin-based polymersbecause they are cost effective and can suppress the change of colormodulation of image quality due to their film uniformity and smallbirefringence wavelength dispersion. Examples of the optical film formedfrom a liquid crystalline material include those comprised of variousliquid crystalline polymeric compounds of main chain- and/or sidechain-types, such as liquid crystalline polyesters, liquid crystallinepolycarbonates, liquid crystalline polyacrylates, or low molecularweight liquid crystalline compounds having reactivities which can bepolymerized by cross-linking or the like after being aligned. Thesefilms may be a single-layered film with self-supportivity or formed overa transparent supporting substrate.

The retardation value of the first optically anisotropic layer at awavelength of 550 nm is so adjusted to be from 210 to 300 nm. Theretardation value is preferably from 250 to 275 nm.

The retardation value of the fourth optically anisotropic layer at awavelength of 550 nm is so adjusted to be from 50 to 140 nm. Theretardation value is preferably from 70 to 120 nm.

The second optically anisotropic layer used in the present invention isa layer comprising at least a liquid crystal film produced by fixing aliquid crystalline polymer exhibiting an optically positive uniaxiality,more specifically a polymeric liquid crystalline compound exhibiting anoptically positive uniaxiality or a polymeric liquid crystal compositioncontaining at least one type selected from the polymeric liquidcrystalline compounds and exhibiting an optically positive uniaxiality,in a nematic hybrid orientation with an average tilt angle of 5 to 45degrees, formed when the liquid crystalline polymeric compound orcomposition is in a liquid crystal state.

The term “nematic hybrid orientation” used herein refers to anorientation structure wherein the liquid crystal molecules are alignedin a nematic orientation wherein the angles of the directors of theliquid crystalline molecules relative to the film upper surface and thelower film surface are different from each other. Therefore, since theangles formed by the directors and the film planes are different betweenin the vicinities of the upper and lower interfaces of the film, thenematic hybrid orientation can be referred to as an orientation whereinthe angles vary continuously between the upper and lower film surfaces.

In a liquid crystal film with a fixed nematic hybrid orientationstructure, the directors of the liquid crystalline molecules aredirected at different angles in all the positions in the film thicknessdirection. Therefore, it can be said that there no longer exists opticalaxis in the whole film structure.

The term “average tilt angle” used herein refers to an average value ofthe angles defined between the directors of the liquid crystallinemolecules and a film plane, in the thickness direction of the liquidcrystal film. In the liquid crystal film used in the present invention,the absolute value of the angle formed by a director in the vicinity ofone of the film surfaces and the film surface is generally from 20 to 90degrees, preferably from 40 to 85 degrees, more preferably from 70 to 80degrees while the absolute value of the angle formed by the director andthe other film surface is generally from 0 to 20 degrees, preferablyfrom 0 to 10 degrees. The absolute value of the average tilt angle isgenerally from 5 to 45 degrees, preferably from 20 to 45 degrees, morepreferably from 25 to 43 degrees, most preferably from 36 to 40 degrees.The average tilt angle, if deviating from the above ranges, would causethe contrast of the resulting liquid crystal display device to decreasewhen the device is viewed from an oblique direction. The average tiltangle can be determined by applying a crystal rotation method.

The liquid crystal film forming the second optically anisotropic layerused in the present invention may be formed from any liquid crystallinematerial as long as the material can be fixed in a nematic hybridorientation with the specific average tilt angle, as described above.For example, the film may be a liquid crystal film produced by allowinga low molecular weight liquid crystalline substance to be in a liquidcrystal state, and then aligning the substance in a nematic hybridorientation and fixing the aligned orientation by photo- orthermal-cross-linking or a liquid crystal film produced by allowing apolymeric liquid crystalline substance to be in a liquid crystal stateand then aligning the substance in a nematic hybrid orientation andfixing the aligned orientation by cooling. The term “liquid crystalfilm” used herein refers to those produced by forming a liquidcrystalline substance such as a low molecular weight or polymeric liquidcrystalline substance into a film, regardless of whether or not theliquid crystal film itself exhibits liquid crystallinity.

The thickness of the liquid crystal film to exhibit more suitableviewing angle improving effect for the liquid crystal display devicevaries depending on the display mode thereof or various opticalparameters but is usually from 0.2 to 10 μm, preferably from 0.3 to 5μm, particularly preferably from 0.5 to 2 μm. A film thickness of lessthan 0.2 μm would fail to attain a sufficient compensation effect. Afilm thickness of greater than 10 μm would cause unnecessary coloredimage in the liquid crystal display device.

With regard to an apparent retardation value in the plane of a liquidcrystal film when viewed from the normal direction thereof, therefractive index (ne) in the direction parallel to directors isdifferent from the refractive index (no) in the direction perpendicularto directors, in a liquid crystal film with a fixed nematic hybridorientation structure and, therefore, assuming that the value obtainedby subtracting no from ne (ne−no) is an apparent birefringence, anapparent retardation value is given as the product of the apparentbirefringence and the absolute film thickness. This apparent retardationvalue is easily obtained by a polarization optical measurement such asellipsometry. The retardation value of the liquid crystal film used as acompensation element is usually from 10 to 400 nm, preferably from 30 to200 nm, particularly preferably from 50 to 140 nm with respect to amonochromic light of 550 nm. A retardation value of smaller than 10 nmwould result in failure to attain a sufficient viewing angle enlargingeffect. A retardation value of larger than 400 nm would causeunnecessary coloration on the liquid crystal display device when viewedobliquely.

The specific conditions for the arrangement of the optical anisotropiclayers in the liquid crystal display device of the present inventionwill be described in more details. In order to describe the specificarrangement conditions, the upper and lower planes and tilt direction ofthe optically anisotropic layer formed of a liquid crystal film and thepre-tilt direction of the liquid crystal cell are defined as followsusing FIGS. 1 to 3.

When the upper and lower planes of the optically anisotropic layerformed of the liquid crystal film are defined by the angles formed bythe directors of the liquid crystalline molecules in the vicinity of thefilm interfaces and the film planes, the plane forming an angle of 20 to90 degrees at the acute angle side with the director is defined as“b-plane”, while the plane forming an angle of 0 to 20 degrees at theacute angle side with the director is defined as “c-plane”.

When c-plane is viewed from b-plane through the optically anisotropiclayer, the direction in which the angles between the directors of theliquid crystal molecules and the projection thereof to the c-plane areacute and which is parallel to the projection is defined as “tiltdirection” (see FIGS. 1 and 2).

Next, on the cell interface of the liquid crystal cell, the lowmolecular weight liquid crystal for driving the liquid crystal cell isnot generally parallel to the cell interface and tilted at a certainangle, which angle is generally referred to as “pre-tilt angle”.However, a direction along which the director of a liquid crystallinemolecule on the cell interface and the projection thereof form an acuteangle and which is parallel to the projection is herein defined as“pre-tilt direction of the liquid crystal cell” (see FIG. 3).

The third optically anisotropic layer used in the present invention isnegative in refractive index anisotropy, i.e., satisfies the requirementdefined by formula (1) below, and preferably the nx and ny of the thirdoptically anisotropic layer are substantially equal to one another. Thethird optically anisotropic layer is preferably from 0 to 30 nm, morepreferably from 0 to 10 nm in Re (retardation in the plane direction ata wavelength of 550 nm) defined by formula (2) below. The thirdoptically anisotropic layer is also preferably from −200 to −30 nm, morepreferably from −150 to −50 nm in Rth (retardation in the thicknessdirection at a wavelength of 550 nm) defined by formula (3) below.nx≧ny>nz  (1)Re=(nx−ny)×d  (2)Rth={nz−(nx+ny)/2}×d  (3)wherein nx and ny denote principal indices of plane direction refractionof the optically anisotropic layer, nz denotes a principal index ofthickness direction refraction of the optically anisotropic layer, and ddenotes the thickness (nm) thereof.

In the present invention, the third optically anisotropic layer may beformed of a single layer or multi layers as long as it exhibits anegative optical anisotropy and satisfies the requirement defined byformula (1). The third optically anisotropic layer may be a polymer filmwherein optical anisotropy is exhibited or any of those wherein opticalanisotropy is exhibited by aligning liquid crystalline molecules. Whenthe third optically anisotropic element is a polymer film, examplesthereof include triacetyl cellulose, polyamides, polyimides, polyesters,polyetherketones, polyamideimides, polyesterimides, and modifiedpolycarbonates. There is no particular restriction on these materialsand any material other than these material can be used if it can assumean aligned state of polymer molecule chain as in the case with thealigned state of the molecular chain of the foregoing materials. Amongthese materials, preferred are polymer films formed from triacetylcellulose or polyimides. Polymer films may be biaxially stretched so asto exhibit the desired Rth. Alternatively, Rth may be adjusted by addingadditives to a polymer. Japanese Patent Laid-Open Publication Nos.2000-111914 and 2001-166144 disclose techniques for adjusting the Rth oftriacetyl cellulose.

When the third optically anisotropic layer is formed from liquidcrystalline molecules, it is formed from preferably discotic liquidcrystalline molecules or cholesteric liquid crystalline molecules, morepreferably discotic liquid crystalline molecules. Aligning of discoticliquid crystalline molecules substantially horizontally with respect toa substrate renders it possible to form a layer exhibiting a negativeoptical anisotropy. Such an alignment technique is disclosed in JapanesePatent Laid-Open Publication No. 11-352328 and also can be utilized inthe present invention. The term “substantially horizontally” means thatthe average angle formed by the optical axis of a discotic liquidcrystalline molecule and the normal direction of a substrate is withinthe range of 0±10 degrees. Discotic liquid crystalline molecules may beobliquely aligned at an average tilt angle of not 0 degree (specificallywithin the range of 0110 degrees) or may be aligned in a hybridorientation wherein tilt angle gradually changes. Alternatively, theforegoing aligned state may be deformed to be twisted by adding a chiraldopant or applying shear stress.

Cholesteric liquid crystalline molecules exhibit a negative opticalanisotropy with their helical twisted orientation. Aligning helicallycholesteric liquid crystalline molecules and controlling the twist angleor retardation value render it possible to obtain desired opticalcharacteristics. Cholesteric liquid crystalline molecules can be alignedin a twisted orientation with a conventional manner.

Liquid crystalline molecules are preferably fixed in an aligned stateand more preferably fixed therein by polymerization.

Description will be given of preferable discotic liquid crystallinemolecules forming the third optically anisotropic layer. Discotic liquidcrystalline molecules are preferably aligned substantially horizontally(average tilt angle within the range of 0 to 40 degrees) to a polymerfilm plane. Discotic liquid crystalline molecules may be obliquelyaligned or may be aligned so that the tilt angle will gradually change(hybrid orientation). For either of the tilt orientation or the hybridorientation, the average tilt angle is preferably from 0 to 40 degrees.Discotic liquid crystalline molecules are described in variousliteratures (Mol. Cryst. Liq. Cryst., vol. 71, page 111 (1981), C.Destrade et al.; Quarterly Chemistry Survey, No. 22, The Chemistry ofLiquid Crystals, Chapter 5, Chapter 10, Section 2 (1994), edited byJapan Chem. Soc.; Angew. Chem. Soc. Chem. Comm., page 1794 (1985), B.Kohne et al.; J. Am. Chem. Soc., vol. 116, page 2,655 (1994), J. Zhanget al. Polymerization of discotic liquid-crystal molecules is describedin Japanese Patent Laid-Open Publication No. 8-27284. In order to fixdiscotic liquid crystalline molecules by polymerization, a polymerizablegroup should be bound to a discotic core of the discotic liquidcrystalline molecules. However, if the polymerizable group is directlybound to the discotic core, it is difficult to keep the alignment at thepolymerization reaction. Therefore, a linking group is introducedbetween the discotic core and the polymerizable group. Discotic liquidcrystalline molecule having a polymerizable group is described inJapanese Patent Laid-Open Publication No. 2001-4387.

The above-described first, second, third and fourth opticallyanisotropic layers may be attached to each other via an adhesive ortacky adhesive layer.

There is no particular restriction on adhesives for forming the adhesivelayer as long as they have enough adhesivity to the opticallyanisotropic layers and do not harm the optical characteristics ofthereof. Examples of the adhesives include acrylic resin-, methacrylicresin-, epoxy resin-, ethylene-vinyl acetate copolymer-, rubber-,urethane-, polyvinylether-based adhesives, and mixtures thereof andvarious reactive adhesives such as of thermal curing and/or photo curingtypes, and electron radiation curing types. The adhesive may be anadhesive having a function of a transparent protective layer forprotecting the optically anisotropic layers.

There is no particular restriction on tacky adhesives for forming thetacky adhesive layer. There may be used any tacky adhesive appropriatelyselected from those containing a polymer such as an acrylic polymer, asilicone-based polymer, a polyester, a polyurethane, a polyamide, apolyether, a fluorine- or rubber-based polymer as a base polymer. Inparticular, it is preferred to use a tacky adhesive such as an acrylictacky adhesive which is excellent in optical transparency, weatherresistance and heat resistance and exhibits tackiness characteristicssuch as moderate wettability, cohesivity and adhesivity.

The adhesive layer or tacky adhesive layer may be formed by any suitablemethod. Examples of the method include a method wherein a base polymeror a composition thereof is dissolved or dispersed in a solventcontaining toluene or ethyl acetate alone or in combination therebypreparing a tacky adhesive or adhesive solution containing 10 to 40percent by mass of the tacky adhesive or adhesive, which solution isthen directly laid over the above-described optically anisotropic layerby an appropriate developing method such as casting or coating or amethod wherein a tacky adhesive or adhesive layer is formed inaccordance with the method as described above on a separator and thentransferred onto the optically anisotropic layers. The tacky adhesive oradhesive layer may contain additives such as natural or syntheticresins, in particular fillers or pigments containing tackiness-impartingresins, glass fibers, glass beads, metal powders, and other inorganicpowders, dyes, and anti-oxidants. The tacky adhesive or adhesive layermay contain fine particles so as to exhibit light diffusivity.

When the optically anisotropic layers are attached to each other via atacky adhesive or adhesive layer, they may be subjected to a surfacetreatment so as to improve their adhesivity to the tacky adhesive oradhesive layer. There is no particular restriction on the method of thesurface treatment. There may be suitably used a surface treatment suchas corona discharge, sputtering, low-pressure UV irradiation, or plasmatreatment, which can maintain the transparency of the liquid crystalfilm surface. Among these surface treatments, corona discharge treatmentis excellent.

Next, description will be given of the configurations of the liquidcrystal display devices comprising the above-described members,according to the present invention.

The configurations of the liquid crystal display devices of the presentinvention are necessarily selected from the following four patterns asshown in FIGS. 4, 7, 10 and 13:

-   -   (A) polarizer/first optically anisotropic layer/fourth optically        anisotropic layer/liquid crystal cell/third optically        anisotropic layer/second optically anisotropic layer/first        optically anisotropic layer/polarizer/backlight;    -   (B) polarizer/first optically anisotropic layer/fourth optically        anisotropic layer/third optically anisotropic layer/liquid        crystal cell/second optically anisotropic layer/first optically        anisotropic layer/polarizer/backlight    -   (C) polarizer/first optically anisotropic layer/second optically        anisotropic layer/liquid crystal cell/third optically        anisotropic layer/fourth optically anisotropic layer/first        optically anisotropic layer/polarizer/backlight    -   (D) polarizer/first optically anisotropic layer/second optically        anisotropic layer/third optically anisotropic layer/liquid        crystal cell/fourth optically anisotropic layer/first optically        anisotropic layer/polarizer/backlight.

The angle formed by the pre-tilt direction of the liquid crystal layerin the liquid crystal cell and the tilt direction of the secondoptically anisotropic layer formed of a liquid crystal film wherein anematic hybrid orientation is fixed is preferably from 0 to 30 degrees,more preferably 0 to 20 degrees, particularly preferably from 0 to 10degrees. The angle of larger than 30 degrees would fail to attain asufficient viewing angle compensation effect.

The angle formed by the slow axis of the first optically anisotropiclayer and the tilt direction of the second optically anisotropic layeris preferably 50 degrees or larger and smaller than 80 degrees, morepreferably 55 degrees or larger and smaller than 75 degrees. The angleof 80 degrees or larger or smaller than 55 degrees would cause areduction in front contrast.

The angle formed by the slow axis of the first optically anisotropiclayer and the slow axis of the fourth optically anisotropic layer ispreferably 50 degrees or larger and smaller than 80 degrees, morepreferably 55 degrees or larger and smaller than 75 degrees. The angleof larger than 80 degrees or smaller than 55 degrees would cause areduction in front contrast.

There is no particular restriction on the aforesaid light diffusionlayer, backlight, light controlling film, light guide plate and prismsheet, which may be those that have been conventionally used.

In addition to the above-described components, the liquid crystaldisplay device of the present invention may be provided with otheradditional components. For example, the use of a color filter makes itpossible to produce a color liquid crystal display device which canprovide multi- or full-colored display images with increased colorpurity.

Effects of the Invention

The liquid crystal display device of the present invention has featuresthat it is bright in displaying, high in front contrast and less inviewing angle dependency. The provision of a reflection layer in part ofthe liquid crystal cell renders it possible to produce a transflectiveliquid crystal display device which can display bright images and ishigh in contras and less in viewing angle dependency in the transmissionmode.

EXAMPLES

The present invention will be further described in the followingexamples, but the present invention should not be construed as beinglimited thereto. The retardations (Δnd) in the examples are values at awavelength of 550 nm, unless stated otherwise.

(Preparation of Third Optically Anisotropic Layer 13)

A polyimide with a weight-average molecular weight (Mw) of 70000 and aΔn of about 0.04 was synthesized from2,2′-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) and2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl (TFMB). On a 80 μm thicktriacetyl cellulose was coated a solution of 25 percent by mass of thepolyimide prepared using cyclohexanone as a solvent. The coatedtriacetyl cellulose was heated at a temperature of 150° C. for 5 minutesthereby producing a totally transparent smooth film 13. The film had aretardation in the plane Re=1 nm, a retardation in the thicknessdirection Rth=−100 nm, and nx÷ny>nz.

Example 1

The configuration and axis arrangement of the liquid crystal displaydevice of Example 1 will be described with reference to FIGS. 4 and 5,respectively.

On a substrate 1 is arranged a transparent electrode 3 formed from ahighly transmissive material such as ITO while on a substrate 2 is acounter electrode 4 formed from a highly transmissive material such asITO. A liquid crystal layer 5 formed from a liquid crystalline materialexhibiting positive dielectric constant anisotropy is sandwiched betweenthe transparent electrode 3 and the counter electrode 4. A fourthoptically anisotropic layer 9, a first optically anisotropic layer 10and a polarizer 7 are arranged on the side of the substrate 2, oppositeto the side on which the counter electrode 4 is formed while a thirdoptically anisotropic layer 13, a second optically anisotropic layer 11,a first optically anisotropic layer 12 and a polarizer 8 are arranged onthe side of the substrate 1, opposite to the side on which thetransparent electrode 3 is formed. A backlight 14 is arranged in therear side of the polarizer 8, as viewed from the viewer.

In accordance with the disclosures of Japanese Patent Laid-OpenPublication No. 6-347742, the second optically anisotropic layer 11 wasprepared which layer was formed of a 0.86 μm thick liquid crystal filmwith a fixed nematic hybrid orientation wherein the average tilt anglein the film thickness direction was 40 degrees. A liquid crystal displaydevice was produced so as to have the axis arrangement as shown in FIG.5.

The liquid crystal cell 6 used in this example was produced usingZLI-1695 manufactured by Merck Ltd as a liquid crystalline material sothat the liquid crystal layer thickness was 4.9 μm. The pre-tilt angleat both of the cell interfaces was 2 degrees, while the Δnd of theliquid crystal cell was approximately 320 nm.

The polarizer 7 (thickness: about 100 μm; SQW-062 manufactured bySumitomo Chemical Industry Co., Ltd.) was disposed on the viewer's side(the upper portion in FIG. 4) of the liquid crystal cell 6. Between thepolarizer 7 and the liquid crystal cell 6 were disposed a polymericstretched film formed of a uniaxially stretched norbornene copolymerfilm as the first optically anisotropic layer 10 and a polymericstretched film formed of a uniaxially stretched norbornene copolymerfilm as the fourth optically anisotropic layer 9. The Δnd of thepolymeric stretched film 10 was approximately 270 nm while the Δnd ofthe polymeric stretched film 9 was approximately 110 nm.

In the rear of the liquid crystal cell 6 viewed from the viewer werearranged a negative film with Rth=−100 nm produced above as the thirdoptically anisotropic layer 13, a liquid crystal film as the secondoptically anisotropic layer 11 and a polymeric stretched film formed ofa uniaxially stretched norbornene copolymer film as the first opticallyanisotropic layer 12, on the back of which a polarizer 8 was arranged.The Δnd of the liquid crystal film 11 with a fixed nematic hybridorientation was 105 nm while the Δnd of the uniaxially stretchedpolymeric film 12 was 265 nm.

The absorption axes of the polarizers 7, 8, the slow axes of thepolymeric stretched films 9, and 12, the pre-tilt direction of theliquid crystal cell 6 at both of the interfaces and the tilt directionof the liquid crystal film 11 were oriented as shown in FIG. 5.

FIG. 6 shows the contrast ratio from all the directions defined by thetransmissivity ratio of white image 0 V and black image 5 V “(whiteimage)/(black image)” when the backlight is on. The concentric circlesare drawn to be at an interval of 20 degrees. Therefore, the outermostcircle indicates 80 degrees from the center.

It was confirmed from FIG. 6 that the liquid crystal display device hadexcellent viewing angle characteristics.

Example 2

The configuration and axis arrangement of the liquid crystal displaydevice of Example 2 will be described with reference to FIGS. 7 and 8,respectively.

The liquid crystal cell 6 of Example 1 is used. On the side of thesubstrate 2 opposite to the side on which the counter electrode 4 isformed are arranged a third optically anisotropic layer 13, a fourthoptically anisotropic layer 15, a first optically anisotropic layer 16and a polarizer 7. On the side of the substrate 1 opposite to the sideon which the transparent electrode 3 is formed are arranged a secondoptically anisotropic layer 11, a first optically anisotropic layer 17and a polarizer 8. A backlight 14 was arranged in the rear of thepolarizer 8.

The polarizers 7,8, the second optically anisotropic layer 11, and thethird optically anisotropic layer 13 are the same as those used inExample 1.

The polarizer 7 was disposed on the viewer's side (the upper portion inFIG. 7) of the liquid crystal cell 6. Between the polarizer 7 and theliquid crystal cell 6 were disposed a polymeric stretched film formed ofa uniaxially stretched norbornene copolymer film as the first opticallyanisotropic layer 16, a polymeric stretched film formed of a uniaxiallystretched norbornene copolymer film as the fourth optically anisotropiclayer 15 and a negative film 13 with Rth=−100 nm produced above as thethird optically anisotropic layer 13. The Δnd of the polymeric stretchedfilm 16 was approximately 270 nm while the Δnd of the polymericstretched film 15 was approximately 110 nm.

In the rear of the liquid crystal cell 6 viewed from the viewer werearranged a liquid crystal film as the second optically anisotropic layer11 and a polymeric stretched film formed of a uniaxially stretchednorbornene copolymer film as the first optically anisotropic layer 17,on the back of which a polarizer 8 was arranged. The Δnd of the liquidcrystal film 11 with a fixed nematic hybrid orientation was 105 nm whilethe Δnd of the uniaxially stretched polymeric film 17 was 265 nm.

The absorption axes of the polarizers 7, 8, the slow axes of thepolymeric stretched films 15, 16 and 17, the pre-tilt direction of theliquid crystal cell 6 at both of the interfaces and the tilt directionof the liquid crystal film 11 were oriented as shown in FIG. 8.

FIG. 9 shows the contrast ratio from all the directions defined by thetransmissivity ratio of white image 0 V and black image 5 V “(whiteimage)/(black image)” when the backlight is on. The concentric circlesare drawn to be at an interval of 20 degrees. Therefore, the outermostcircle indicates 80 degrees from the center.

It was confirmed from FIG. 9 that the liquid crystal display device hadexcellent viewing angle characteristics.

Example 3

The configuration and axis arrangement of the liquid crystal displaydevice of Example 3 will be described with reference to FIGS. 10 and 11,respectively.

The liquid crystal cell 6 of Example 1 is used. On the side of thesubstrate 2 opposite to the side on which the counter electrode 4 isformed are arranged a second optically anisotropic layer 11, a firstoptically anisotropic layer 18 and a polarizer 7. On the side of thesubstrate 1 opposite to the side on which the transparent electrode 3 isformed are arranged a third optically anisotropic layer 13, a fourthoptically anisotropic layer 19, a first optically anisotropic layer 20and a polarizer 8. A backlight 14 is arranged in the rear of thepolarizer 8.

The polarizers 7,8, the second optically anisotropic layer 11, and thethird optically anisotropic layer 13 were the same as those used inExample 1.

The polarizer 7 was disposed on the viewer's side (the upper portion inFIG. 10) of the liquid crystal cell 6. Between the polarizer 7 and theliquid crystal cell 6 are disposed a polymeric stretched film formed ofa uniaxially stretched norbornene copolymer film as the first opticallyanisotropic layer 18 and a liquid crystal film as the second opticallyanisotropic layer 11. The Δnd of the polymeric stretched film 18 wasapproximately 265 nm while the Δnd of the liquid crystal film 11 with afixed hybrid nematic orientation was approximately 105 nm.

In the rear of the liquid crystal cell 6 viewed from the viewer werearranged a negative film with Rth=−100 nm produced above as the thirdoptically anisotropic layer 13, a polymeric stretched film formed of auniaxially stretched norbornene copolymer film as the fourth opticallyanisotropic layer 19 and a polymeric stretched film formed of auniaxially stretched norbornene copolymer film as the first opticallyanisotropic layer 20, on the back of which the polarizer 8 was arranged.The And of the uniaxially stretched polymeric film 19 was 110 nm whilethe Δnd of the uniaxially stretched polymeric film 20 was 270 nm.

The absorption axes of the polarizers 7, 8, the slow axes of thepolymeric stretched films 18, 19 and 20, the pre-tilt direction of theliquid crystal cell 6 at both of the interfaces and the tilt directionof the liquid crystal film 11 were oriented as shown in FIG. 11.

FIG. 12 shows the contrast ratio from all the directions defined by thetransmissivity ratio of white image 0 V and black image 5 V “(whiteimage)/(black image)” when the backlight is on. The concentric circlesare drawn to be at an interval of 20 degrees. Therefore, the outermostcircle indicates 80 degrees from the center.

It was confirmed from FIG. 12 that the liquid crystal display device hadexcellent viewing angle characteristics.

Example 4

The configuration and axis arrangement of the liquid crystal displaydevice of Example 4 will be described with reference to FIGS. 13 and 14,respectively.

The liquid crystal cell 6 of Example 1 is used. On the side of thesubstrate 2 opposite to the side on which the counter electrode 4 isformed are arranged a third optically anisotropic layer 13, a secondoptically anisotropic layer 11, a first optically anisotropic layer 21and a polarizer 7. On the side of the substrate 1 opposite to the sideon which the transparent electrode 3 is formed are arranged a fourthoptically anisotropic layer 22, a first optically anisotropic layer 23and a polarizer 8. A backlight 14 is arranged in the rear of thepolarizer 8.

The polarizers 7,8, the second optically anisotropic layer 11, and thethird optically anisotropic layer 13 are the same as those used inExample 1.

The polarizer 7 was disposed on the viewer's side (the upper portion inFIG. 13) of the liquid crystal cell 6. Between the polarizer 7 and theliquid crystal cell 6 were disposed a polymeric stretched film formed ofa uniaxially stretched norbornene copolymer film as the first opticallyanisotropic layer 21, a liquid crystal film as the second opticallyanisotropic layer 11 and a negative film with Rth=−100 nm produced aboveas the third optically anisotropic layer 13. The Δnd of the polymericstretched film 21 was approximately 265 nm while the Δnd of the liquidcrystal film 11 with a fixed hybrid nematic orientation wasapproximately 105 nm.

In the rear of the liquid crystal cell 6 viewed from the viewer werearranged a polymeric stretched film formed of a uniaxially stretchednorbornene copolymer film as the fourth optically anisotropic layer 22and a polymeric stretched film formed of a uniaxially stretchednorbornene copolymer film as the first optically anisotropic layer 23,on the back of which the polarizer 8 was arranged. The Δnd of theuniaxially stretched polymeric film 22 was 110 nm while the Δnd of theuniaxially stretched polymeric film 23 was 270 nm.

The absorption axes of the polarizers 7, 8, the slow axes of thepolymeric stretched films 21, 22 and 23, the pre-tilt direction of theliquid crystal cell 6 at both of the interfaces and the tilt directionof the liquid crystal film 11 were oriented as shown in FIG. 14.

FIG. 15 shows the contrast ratio from all the directions defined by thetransmissivity ratio of white image 0 V and black image 5 V “(whiteimage)/(black image)” when the backlight is on. The concentric circlesare drawn to be at an interval of 20 degrees. Therefore, the outermostcircle indicates 80 degrees from the center.

It was confirmed from FIG. 15 that the liquid crystal display device hadexcellent viewing angle characteristics.

Comparative Example 1

The configuration of the liquid crystal display device of ComparativeExample 1 will be described with reference to FIG. 16.

The liquid crystal display device of this example was produced with thesame procedures of Example 1 except that the third optically anisotropiclayer 13 was excluded.

FIG. 17 shows the contrast ratio from all the directions defined by thetransmissivity ratio of white image 0 V and black image 5 V “(whiteimage)/(black image)” when the backlight is on. The concentric circlesare drawn to be at an interval of 20 degrees. Therefore, the outermostcircle indicates 80 degrees from the center.

With regard to viewing angle characteristics, Example 1 and ComparativeExample 1 are compared.

Comparing the contrast contour lines shown in FIGS. 6 and 17, it isconfirmed that viewing angle characteristics are significantly improvedusing the third optically anisotropic layer 13.

Comparative Example 2

The configuration of the liquid crystal display device of ComparativeExample 2 will be described with reference to FIG. 18.

The liquid crystal display device of this example was produced with thesame procedures of Example 1 except that the fourth opticallyanisotropic layer 9 was shifted from the viewer's side of the liquidcell 6 to the rear side thereof.

However, it was confirmed that contrast was significantly reduced evenwhen the device was viewed from the front and image quality was reducedto an extent that the image was not visible with naked eyes.

Example 5

The configuration of the transflective liquid crystal display device ofExample 5 will be described with reference to FIG. 19.

The liquid crystal display device of this example are produced with thesame procedures of Example 1 except that a liquid crystal cell 24 wasused.

On the substrate 1 of the liquid crystal cell 24 were arranged areflective electrode 25 formed of a highly reflective material such asAl and a transparent electrode 26 formed of a highly transmissivematerial such as ITO. A liquid crystal layer 5 formed from a liquidcrystalline material exhibiting positive dielectric constant anisotropyis sandwiched between the reflective and transparent electrodes 25, 26and the counter electrode 4.

The liquid crystal layer thicknesses of the liquid crystal cell 24 inthe reflective electrode region 25 (reflective display part) and thetransparent electrode region 26 (transmissive display part) were set to2.4 μm and 4.9 μm, respectively. The pre-tilt angle of the liquidcrystal layer at both of the substrate interfaces was 2 degrees. TheΔnds of the liquid crystal cell in the reflective displaying part andtransmissive displaying part are approximately 150 nm and 320 nm,respectively.

With regard to the contour lines from all of the directions, it wasconfirmed that a similar results to that shown in FIG. 6 was obtainedwith this device and a transflective liquid crystal display device witha wide viewing angle was able to be produced.

In these examples, the experiments were carried out without using acolor filter. Of course, the provision of a color filter in the liquidcrystal cell can provide excellent multi-color or full-color images.

APPLICABILITY IN THE INDUSTRY

According to the present invention, there is provided a liquid crystaldisplay device which can provide bright images and is high in frontcontrast and less in viewing angle dependency.

It will be appreciated by those skilled in the art that changes could bemade to the embodiments described above without departing from the broadinventive concept thereof. It is understood, therefore, that thisinvention is not limited to the particular embodiments disclosed, but itis intended to cover modifications within the spirit and scope of thepresent invention as defined by the appended claims.

1. A liquid crystal display device comprising at least: a backlight; apolarizer; a first optically anisotropic layer with a retardation of 210to 300 nm at a wavelength of 550 nm; a second optically anisotropiclayer with a retardation of 50 to 140 nm at a wavelength of 550 nm; athird optically anisotropic layer with negative optical anisotropy; aliquid crystal cell comprising upper and lower substrates facing eachother and a liquid crystal layer sandwiched between the upper and lowersubstrates; a fourth optically anisotropic layer with a retardation of50 to 140 nm at a wavelength of 550 nm; a first optically anisotropiclayer with a retardation of 210 to 300 nm at a wavelength of 550 nm; anda polarizer, arranged in piles in this order from the backlight, thesecond optically anisotropic layer comprising at least a liquid crystalfilm with a fixed nematic hybrid liquid crystal orientation structure.2. The liquid crystal display device according to claim 1, wherein theliquid crystal layer is of a twisted nematic mode.
 3. The liquid crystaldisplay device according to claim 1, wherein the liquid crystal layer isof a parallel orientation with a twist angle of 0 degrees.
 4. The liquidcrystal display device according to claim 1, wherein the third opticallyanisotropic layer fulfills the requirement set forth in formula (1) andhas a plane direction retardation (Re) in the range of 0 nm to 30 nm anda thickness direction retardation (Rth) in the range of −200 nm to −30nm, both at a wavelength of 550 nm, when (Re) and (Rth) are representedby formulas (2) and (3), respectively:nx≧ny>nz  (1)Re=(nx−ny)xd  (2)Rth={nz−(nx+ny)/2}xd  (3) wherein nx and ny denote principal indices ofplane direction refraction of the optically anisotropic layer, nzdenotes a principal index of thickness direction refraction of theoptically anisotropic layer, and d denotes the thickness (nm) thereof.5. The liquid crystal display device according to claim 1, wherein thethird optically anisotropic layer is formed from at least one type ofmaterial selected from the group consisting of liquid crystallinecompounds, triacetyl cellulose, polyamides, polyimides, polyesters,polyether ketones, polyamide imides, and cyclic olefin polymers.
 6. Theliquid crystal display device according to claim 1, wherein the firstand fourth optically anisotropic layers are stretched polymer films. 7.The liquid crystal display device according to claim 1, wherein thefirst and fourth optically anisotropic layers are each a liquid crystalfilm produced by fixing a liquid crystalline substance exhibiting anoptically positive uniaxiality, in a nematic orientation formed when thesubstance is in the liquid crystal state.
 8. The liquid crystal displaydevice according to claim 1, wherein the angle defined by the tiltdirection of the hybrid direction of the liquid crystal film forming thesecond optically anisotropic layer, projected to a plane and the rubbingdirection of the liquid crystal layer is in the range of 0 to 30degrees.
 9. The liquid crystal display device according to claim 1,wherein the second optically anisotropic layer is a liquid crystal filmproduced by fixing a liquid crystalline substance exhibiting anoptically positive uniaxiality, in a nematic hybrid orientation formedwhen the substance is in the liquid crystal state, and the average tiltangle of the nematic hybrid orientation is in the range of 36 to 45degrees.
 10. The liquid crystal display device according to claim 1,wherein the lower substrate of the liquid crystal cell has atransflective electrode on which a region with a reflective function anda region with a transmissive function are formed.
 11. The liquid crystaldisplay device according to claim 10, wherein the thickness of theliquid crystal layer on the region with a reflective function in theliquid crystal cell is smaller than that of the liquid crystal layer onthe region with a transmissive function.
 12. A liquid crystal displaydevice comprising at least: a backlight; a polarizer; a first opticallyanisotropic layer with a retardation of 210 to 300 nm at a wavelength of550 nm; a second optically anisotropic layer with a retardation of 50 to140 nm at a wavelength of 550 nm; a liquid crystal cell comprising upperand lower substrates facing each other and a liquid crystal layersandwiched between the upper and lower substrates; a third opticallyanisotropic layer with negative optical anisotropy; a fourth opticallyanisotropic layer with a retardation of 50 to 140 nm at a wavelength of550 nm; a first optically anisotropic layer with a retardation of 210 to300 nm at a wavelength of 550 nm; and a polarizer, arranged in piles inthis order from the backlight, the second optically anisotropic layercomprising at least a liquid crystal film with a fixed nematic hybridliquid crystal orientation structure.
 13. A liquid crystal displaydevice comprising at least: a backlight; a polarizer; a first opticallyanisotropic layer with a retardation of 210 to 300 nm at a wavelength of550 nm; a fourth optically anisotropic layer with a retardation of 50 to140 nm at a wavelength of 550 nm; a third optically anisotropic layerwith negative optical anisotropy; a liquid crystal cell comprising upperand lower substrates facing each other and a liquid crystal layersandwiched between the upper and lower substrates; a second opticallyanisotropic layer with a retardation of 50 to 140 nm at a wavelength of550 nm; a first optically anisotropic layer with a retardation of 210 to300 nm at a wavelength of 550 nm; and a polarizer, arranged in piles inthis order from the backlight, the second optically anisotropic layercomprising at least a liquid crystal film with a fixed nematic hybridliquid crystal orientation structure.
 14. A liquid crystal displaydevice comprising at least: a backlight; a polarizer; a first opticallyanisotropic layer with a retardation of 210 to 300 nm at a wavelength of550 nm; a fourth optically anisotropic layer with a retardation of 50 to140 nm at a wavelength of 550 nm; a liquid crystal cell comprising upperand lower substrates facing each other and a liquid crystal layersandwiched between the upper and lower substrates; a third opticallyanisotropic layer with negative optical anisotropy; a second opticallyanisotropic layer with a retardation of 50 to 140 nm at a wavelength of550 nm; a first optically anisotropic layer with a retardation of 210 to300 nm at a wavelength of 550 nm; and a polarizer, arranged in piles inthis order from the backlight, the second optically anisotropic layercomprising at least a liquid crystal film with a fixed nematic hybridliquid crystal orientation structure.